Hi.

In a setting (io field) i can set a value.

I need to detect if this value changes.

An example:

The value is set at 10.0. I change the value to 14.0 from the HMI panel. When the next cycle comes, the PLC "notes" the change in value, and set a bit for one cycle.

How can i make the above ?

Best regards

Stefan

Hello,

use an auxiliary float.

if value is different from aux then set bit and copy value to aux else reset bit.

You can write function and then test it with plcsim

Best Regards

Make another variable HMI_Variable_Old.

At the beginning of your program block, compare HMI_Variable to HMI_Variable OLD.  If they are different, then do whatever you do when the variable changes.

At the end of the program block, set HMI_Variable_Old = HMI_Variable.

S_N

Hi.

In a setting (io field) i can set a value.

I need to detect if this value changes.

An example:

The value is set at 10.0. I change the value to 14.0 from the HMI panel. When the next cycle comes, the PLC "notes" the change in value, and set a bit for one cycle.

How can i make the above ?

Best regards

Stefan

Hi.

<mindware>  and  <Jeff Casagrande>  are basically making the same suggestion. This should be plan A as this is the best suggestion.

Now the following is for plan B..           (triggered by HMI)

At the declaration of the HMI tag,
there is the possibility to trigger a task when..
* the value changes
* the value is above a limit
* the value is below a limit.

For your purpose you could SET a bit when the value changes.
The PLC can then do something and RESET the bit.
This is almost the same type functionality we used on TD200 (S7-200)

The disadvantage of this method is that the "value change" trigger
will also occur when the PLC makes a change to the value.

Is this helpful?
w

William_B

The disadvantage of this method is that the "value change" trigger
will also occur when the PLC makes a change to the value.

 Hello,

if change come from PLC in not a big problem because you can "menage" this change.

The real disadvantage is if some time after the plant startup customer ask to another company <is it possible to change this value also from scada?>

Then customer call you saying <Why your PLC is not working????>.......

I think it is Always better don't create "Dangerous" situation........

As I read in the signature of the user smiffy : 

smiffy

Programming today is the race between software engineers building bigger and better *** proof programs, and the universe producing bigger and better ***s.

So far, the universe is winning...

maybe universe will win ...... but we have to fight......

have a good weekend

Thank you very much for all your help guys.

I have attached my solution, and it works perfect :)